JPH0125012Y2 - - Google Patents

Description

[Detailed Description of the Invention] A VTR as shown in FIG. 1 can be considered as a color VTR with improved S/N ratio of a carrier color signal.

That is, in FIG. 1, during recording, a color video signal is supplied to a low-pass filter 12 through a terminal 11 to extract a luminance signal S _y , and this signal S _y is supplied to an FM modulation circuit 13 to generate an FM signal.
S _f , and this signal S _f is supplied to the adder circuit 14 .

Further, the color video signal from the terminal 11 is supplied to the bandpass filter 21, and the carrier color signal S _s (carrier frequency _s 3.58MHz) is extracted.
S _s is supplied to a pre-emphasis circuit 23 through an ACC circuit 22 .

This pre-emphasis circuit 23 is configured in a feed-forward type by an emphasis signal forming circuit 5 and an adder circuit 6, and the signal _Ss is supplied to the adder circuit 6, and the recording/reproduction changeover switch 8 It is supplied to the emphasis signal forming circuit 5 through the side contact R, and its output signal S _e is supplied to the adding circuit 6. At this time, as shown in FIG. 2, the emphasis circuit 5 has a frequency characteristic with a band elimination characteristic (inverse bell characteristic) centered on the carrier frequency _s , and an input/output characteristic with a nonlinear characteristic. be done.

Therefore, in the carrier color signal _Ss taken out from the adder circuit 6, the outer part of the sideband is enhanced,
That is, the further away from the carrier frequency _s , the more the level is enhanced, and the smaller the original level is, the more the level is enhanced.

and this pre-emphasized carrier color signal.
S _s is supplied to the frequency converter 24 to convert it into an FM signal.
The frequency is converted into a carrier color signal S _c that occupies the lower frequency side of S _f , and at this time, this signal S _c has a carrier frequency or phase such that the frequency is interleaved with each other every one field period. and,
This signal S _c is supplied to the adder circuit 14 .

Therefore, a sum signal S _a of the signals S _f and S _c is taken out from the adder circuit 14 , and this signal S _a passes through the recording amplifier 15 and further through the recording side contact R of the recording/reproduction changeover switch 9 to the rotating magnetic field. Head 1
A and 1B and recorded on the magnetic tape 2.
In this case, the signal S _a is recorded so that one field becomes one diagonal magnetic track, and adjacent magnetic tracks touch each other, and the azimuth angles of heads 1A and 1B are different from each other. As a result, adjacent magnetic tracks have different azimuth angles.

On the other hand, during playback, the heads 1A and 1B play back the signal S _a from the tape 2, and this signal S _a is supplied to the high-pass filter 32 through the playback side contact P of the switch 9 and further through the playback amplifier 31.
The FM signal S _f is taken out, and this signal S _f is supplied to the FM demodulation circuit 34 through the limiter 33 to demodulate the luminance signal S _y , and this signal S _y is supplied to the addition circuit 35.

Further, the signal S _a from the amplifier 31 is supplied to the low-pass filter 41 to extract the carrier color signal S _c , and this signal S _c is supplied to the frequency converter 43 through the ACC circuit 42 and the AFC/
An alternating signal is supplied from the APC circuit 44 and the signal S _c
The signal S _s is frequency-converted to the original carrier color signal S s , and this signal S _s is supplied to a C-shaped comb filter 45 to remove the inter-track crosstalk component, and the signal S _s from which this crosstalk component has been removed is The signal is supplied to a de-emphasis circuit 46.

This de-emphasis circuit 46 is configured in a feedback type by an emphasis signal forming circuit 5 and a subtracting circuit 7, and the output signal of the subtracting circuit 7 is supplied to the emphasis signal forming circuit 5 through the reproduction side contact P of the switch 8. its output signal
S _e is supplied to the subtraction circuit 7. Therefore, the de-emphasis circuit 46 is similar to the pre-emphasis circuit 23.
The carrier color signal S _s has a characteristic complementary to that of the carrier color signal S s , and the outer portion of the sideband that was enhanced during recording is attenuated, and the carrier color signal S _{s becomes the carrier color signal S s} with the original flat frequency characteristic. Also, at this time, the noise component included in the carrier color signal _Ss is attenuated.

Then, the signal S _s with the noise component attenuated is supplied to the adding circuit 35 and added to the signal S _y , and the original color video signal is taken out at the terminal 36.

In this case, the emphasis signal forming circuit 5 is configured as shown in FIG. 3, for example.

That is, the carrier color signal S _s from the ACC circuit 22 or the subtraction circuit 7 is supplied to the base of the transistor Q ₂ through the emitter follower transistor Q ₁ . The emitter of this transistor Q ₂ is grounded, and the carrier frequency is connected to the emitter.
A parallel resonant circuit X ₁ having a resonant frequency _s is provided. Therefore, the frequency characteristics of transistor _Q2 are:
It has a band-elimination characteristic, and the transistor
From the collector of _Q2 , the outer part of the sideband of the carrier color signal _Ss is taken out.

The outside portion of this sideband is then supplied to a limiter formed by transistors Q ₃ and Q ₄ to have non-linear characteristics. A signal S _e is therefore obtained at the collector of the transistor Q ₃ , which signal S _e is taken out through the emitter follower transistor Q ₅ .

In this way, in the VTR shown in FIG. 1, the carrier color signal S _s is de-emphasized during playback, so that
Even if a noise component is included in the carrier color signal S _s due to recording and reproduction, the noise component, especially the high frequency component, is suppressed and removed, resulting in a carrier color signal S _s with a good S/N ratio. Furthermore, since the pre-emphasis circuit 23 and the de-emphasis circuit 46 are configured with complementary characteristics,
There is no change in the amplitude or phase of the carrier color signal _Ss .

By the way, when implementing the emphasis signal forming circuit 5 in FIG. 3 into an IC, the part surrounded by the chain line is
It can be made into a chip IC, but it is a coupling capacitor.
Since C ₁ and resonance circuit X ₁ cannot be integrated into an IC, they are attached externally to the IC. Therefore, the IC requires two additional external terminals T ₁ and T ₂ .

Also, even if the part surrounded by the chain line is made into an IC, there are many external components, so the merit of making it into an IC is reduced (transistor _Q2 can be made into an IC, but doing so would require three external terminals).

This invention attempts to eliminate these problems.

Therefore, in this invention, the emphasis signal forming circuit 5 is configured as shown in FIG. 4, for example.

That is, the carrier color signal S _s from the ACC circuit 22 or the subtraction circuit 7 is supplied to the base of the transistor Q ₁₁ , and the constant current source _{A 11 is} connected to the emitter of the transistor Q _{11 .}
is considered to be Emitsuta Folowa. The emitter of transistor Q ₁₁ is connected to the bases of transistors Q ₁₂ and Q ₁₃ through resistors R ₁₁ and R ₁₂ , and the emitters of transistors Q ₁₂ and Q ₁₃ are commonly connected to constant current source A ₁₂ and are non-wired. A linear circuit, for example a limiter 51, is configured.

Furthermore, the base of the transistor Q ₁₃ is connected to a bandpass filter whose pass band is mainly around the center of the carrier color signal S _s through a DC cut capacitor C ₁₁ , such as a parallel resonant circuit X ₁₁ whose resonance frequency is the carrier frequency _s . At the same time, an emitter follower transistor _Q14 is connected to the collector of the transistor _Q13 . Note that A ₁₃ is a constant current source.

In addition, in this emphasis signal forming circuit 5, the part surrounded by the chain line is made into a single chip IC, and a resonant circuit is formed.
_X11 is connected externally to the IC through external terminal _T11 .

According to such a configuration, the carrier color signal S _s supplied to the transistor Q ₁₁ is supplied from its emitter through the resistor R ₁₁ to the base of the transistor Q ₁₂ . Also, at this time, the signal S _s at the emitter of the transistor Q ₁₁ should also be supplied to the base of the transistor Q ₁₃ through the resistor R ₁₂ , but since the resonant circuit X ₁₁ is connected to the base, The part of the signal S _s outside the sideband is bypassed through the resonant circuit X ₁₁ and the signal S _s
Only the component near the center of is fed to the base of transistor _Q13 .

Therefore, the difference component between the base inputs of the transistors _{Q 12 and} Q ₁₃ , that is, the portion outside the side band of the signal S _s is taken out to the collector of the transistor Q 13.

Furthermore, in this case, the transistors Q ₁₂ and Q ₁₃ constitute the limiter 51 and their input/output characteristics are non-linear, so the portion outside the sideband of the signal S _s obtained at the collector of the transistor Q ₁₃ is
The smaller the level of the signal S _s is, the more the level is enhanced.

The signal available at the collector of transistor _Q13 is therefore the emphasis signal S _e , which is tapped off through transistor _Q14 .

In this case, according to this invention, as is clear from Figure 4, it is possible to reduce the number of external terminals when integrated into an IC, and also to reduce the number of external parts. The benefits are great.

Furthermore, by connecting a resistor in series with the resonant circuit _X11 , the gain of the limiter 51 can be changed.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining this invention, and FIG. 4 is a connection diagram of an example of this invention. 51 is a nonlinear circuit.

Claims (1)

[Claim for Utility Model Registration] During recording, the luminance signal is converted to an FM signal, the carrier color signal is pre-emphasized, and then the frequency is converted to a lower frequency range than the above FM signal, and this low frequency converted carrier color signal and the above FM signal. The added signal is supplied to a rotating magnetic head to be recorded on a magnetic tape, and during playback, the added signal is played back from the magnetic tape by the rotating magnetic head to generate the FM signal and the low frequency converted carrier color signal. The luminance signal is demodulated and extracted from the separated FM signal, the frequency of the separated carrier color signal is converted to the original band at the time of recording, and the frequency-converted carrier color signal is de-emphasized. The color VTR that is taken out includes a limiter in which first and second transistors are differentially connected, a parallel resonant circuit whose resonant frequency is the carrier frequency of the carrier color signal, an adder circuit, and a subtracter circuit. and the parallel resonant circuit is connected between the base of the second transistor and ground, and during the recording, the carrier color signal is supplied to the adder circuit and the base of the first transistor. and the pre-emphasized carrier color signal is supplied to the base of the second transistor through a resistor, and the collector output of the first or second transistor is supplied to the adder circuit to output the pre-emphasized carrier color signal to the output terminal of the adder circuit. During the above-mentioned reproduction, the carrier color signal frequency-converted to the original band is supplied to the above-mentioned subtraction circuit, and the output signal of this subtraction circuit is A signal is supplied to the base of the transistor and also to the base of the second transistor through the resistor, and the collector output of the first or second transistor is supplied to the subtraction circuit so that the output signal of the subtraction circuit is A color VTR that is extracted as the de-emphasized carrier color signal.